NEW  TYPE 
OF  DAM 


CHRONICLE  BUILDING 
SAN  FRANCISCO,  CAL. 


F.  G.  BAUM  & COMPANY 


PAGE  FOUR 


Fig.l 


NEW  TYPE  OE 

ARCH  DAM 

The  service  which  a dam  of  any  type  vis  expected  to  perform  is  that  of 
keeping  water  back,  storing  it  for  future  use,  or  raising  its  level  to  increase 
its  potential  energy.  All  types  do  this  equally  .well.  The  best  type  of  dam 
to  select  for  any  given  locality  will,  therefore,  be  the  one  which  does  this 
in  the  safest  and  cheapest  manner.  The  type  described  below  has  these 
features,  when  constructed  where  ordinary  arched  dams  are  possi- 
ble of  application ; that  is,  in  comparatively  narrow  canyons  where  the 
bottom  and  sides  are  solid  rock.  In  the  design  only  well  known  and  thor- 
oughly practical  principles  have  been  employed.  These  have,  however,  been 
combined  in  a new ‘manner  which  has  brought  theory  and  practice  as  close 
to  each  other  as  is  possible  in  any  structure,  thereby  effecting  a great  saving 
of  material.  The  main  feature  of  this  new  type,  and  the  one  which  makes  the 
high  economy  of  construction  feasible,  is  the  keeping  of  the  subtended  angle 
of  the  arch  as  nearly  constant  as  possible,  and  as  near  to  the  most  economical 
vakie  at  any  elevation,  as  the  contour  of  the  dam  site  will  permit.  This  neces- 
sitates the  abandonment  of  the  constant  up-stream  radius  generally  employed 
in  arch  dams  as  at  present  constructed  ; and  the  substitution  of  radii  of  varying 
length  determined  by  the  width  of  the  canyon  at  any  elevation.  It  will  be 
shown  that  it  is  of  the  highest  importance  that  the  angle  enclosed  by  the  arch 
dam  be  held  as  nearly  constant  as  possible,  at  all  elevations,  the  length  of  the 
radius  of  the  arch  being  fixed  in  accordance  with  this  condition. 


THE  DESIGN 
OF  THE  DAM 

In  designing  the  dam  it  is  convenient  to  start  with  the  assumption  which 
is  usually  made  that  any  unit  horizontal  element  of  a curved  dam,  such  as 
that  for  example  shown  in  Figure  2,  is  a portion  of  a cylindrical  ring,  in  which 
the  average  stress  q,  expressed  in  pounds  per  square  foot,  is  equal  to  the  radial 
load  P (in  pounds  per  square  foot),  multiplied  by  the  radius  of  the  exterior  face 
and  divided  by  the  area  of  the  section  ; as  per  equation  1 : — 

(1)  ,,-Pd^n 

7 A 

in  which  t equals  the  thickness  of  the  dam  at  any  given  point,  R is  the  radius 
of  the  down-stream  face  and  A,  the  area  of  the  section. 


PAGE  FIVE 


Further,  the  volume  of  concrete  in  any  arch  dam  is  equal  to  the  area 
of  the  clam  section,  times  the  mean  radius,  times  the  enclosed  angle. 

(2)  V —A.  x R,„x  2 ft 

V being  the  volume,  Rm  the  mean  radius,  26  the  enclosed  angle  indicated 
in  figure  2. 


AVy/.  Z 


The  mean  radius  Rm,  equals  the  radius  of  the  down-stream  face  plus 
half  the  thickness  t;  and  also  equals  half  the  width  W,  of  the  canyon  divided 
by  the  sine  of  half  the  subtended  angle. 


(3) 


/ >V 

&”•  = sirTd 


Now  as  the  area  of  the  dam  section  varies  with  the  mean  radius ; the 
volume  of  masonry  is:— - 


(4) 


V= 


C x(rjx  2ft 

>7/7.  'ft 


/\X  ft 

sm. ' ft 


in  which  C1  and  K are  constants,  the  latter  depending  upon  the  width  of 
the  canyon. 
page  six 


From  equation  4 it  is  seen  that  the  volume  varies  with 

ft 

sin2  (i 

The  relative  values  of  this  term  are  graphically  shown  by  the  curve  3,  in 
wiiich  the  various  angles  representing  26  constitute  the  abscissas  and  the 
values  of 

* 

0 

S"V ft 


constitute  the  ordinates ; the  latter  for  reasons  above  set  forth  being 
proportional  to  the  volume  of  the  masonry.  From  this  curve  it 
will  be  seen  that  the  amount  of  masonry  required  for  any  curved  or  arched 
dam  will  be  a minimum  when  the  mean  radius  at  any  elevation  is  so  chosen 
that  the  enclosed  angle  26  is  about  I33°;  .and  the  curve  also  shows  that  the 
variation  in  the  amount  of  masonry  required  for  a given  dam  will  only  be 
about  one  per  cent,  provided  that  the  values  of  26  be  held  between  the  limits 
of  1200  and  146°. 

The  method  of  dam  design  herein  disclosed  involves  the  inde- 
pendent determination  of  the  dimensions  of  successive  arch-shaped  slices 
of  the  dam  lying  between  predetermined  levels ; each  slice  being  considered 
primarily  as  an  independent  structure ; such  slices  being  thereafter  super- 
posed to  form  the  dam  body. 

Referring  now  to  Figure  1,  the  procedure  for  determining  the  con- 
tour of  the  faces  of  the  dam  therein  shown  is  as  follows : A topo- 
graphical survey  of  the  canyon  or  valley  should  first  be  made  and  the  con- 
tour lines  should  be  plotted  as  indicated  in  Figure  1.  In  the  present  instance 
six  elevations  or  levels  have  been  established,  forming  respectively  the  con- 
tour lines  I,  II,  III,  IV,  V and  VI,  the  contour  line  VI  corresponding  to  the 
level  of  the  water  retained  by  the  dam  when  the  latter  is  completed,  while  the 
coutour  line  I— I corresponds  to  the  lowest  dam  level  in  the  gorge  or  valley; 
the  remaining  lines  being  those  of  intermediate  levels. 

The  distance  across  the  canyon  We  at  the  top  (contour  VI)  Of  the  dam  is 
ascertained.  Then  the  mean  radius, 


which  will  give  the  dam  the  greatest  strength  with  the  least  volume  of 
material  is  found  by  means  of  figure  3.  At  this  particular  elevation  (VI)  the 
most  economical  mean  radius  will  be 


2 

sin.0 

At  the  top  of  the  dam  it  will  generally  be  found  of  advantage  to  choose 
26  near  the  upper  limit  (146°)  for  greatest  economy,  and  at  the  bottom  to  cor- 
respondingly choose  26  near  the  lower  limit  (1200).  After  the  most  economi- 
cal mean  radius  for  this  elevation  has  been  ascertained,  the  thickness  t«  may 
be  algebraically  determined,  from  the  foregoing  equations. 


PAGE  SEVEN 


\ 


o 


«S 


<5> 

£ ^ 


. 3 

S 


S 


1 1 


5 


^ *N 


dt/mioA  jo  d/?MjUdJ./ac/  osj/j  OZJ&  <*> 
sanjnA  judusjjip.ioj  y*  • • jo  ggnyuA 


■§ 

I 

§ 

1 

I 

§ 

*: 

% 

3 

1 

5 

I 


£ 


| 


.S 

I 

5 

■k» 

I 

% 

I 

n 

<s 

S 


c 

§ in 

& 


§ 


Q 

I ^ 

* § 

£ 


5s 

Si 

< 


§ 

I 

I 

Ss 

I 

kfc 


<0 


I 

£ 

1 

§ 


■5  ^ 

js  v 

5-2  <6 

is 

^<fc  -2 

&§ 

''  i ts^ 

8 V* 
s’S^ 

•kj  *>  s 

g § 

§ 

fc  < « 

^1 


K *£} 

<^> 


f<*> 


Sc 

II 

<£ 


K I 
s ^ 

3 

? s \ 

*^>  vN.,  * 

mi 

ilH 


^ ^ s 


s S v * 


II 

5 


8 ^ 
■§  § s < 

? 5 5: : 

lk< 


O ^ ^ 

,S\S  « 

IT'S  ^ 

7 '"  * 
g$  s 

c:  < 3 

sS  ^ 


PAGE  EIGHT 


The  first  relatively  abrupt  change  of  slope  of  the  canyon  sides  occurs 
at  elevation  V.  The  distance  across  the  canyon  at  this  elevation  being  meas- 
ured, the  most  economical  mean  radius  of  the  section  is  found  in  the 
same  manner  as  the  mean  radius  for  Elevation  VI  was  determined.  After  the 
mean  radius  has  been  settled  upon,  the  thickness  ts  is  computed  and 
the  up  and  down  stream  radii  are  determined.  The  center  of  curvature  of  the 
arch  slice  at  elevation  V with  a thickness  U does  not  necessarily  lie  on  the 
same  center  line  as  the  center  of  curvature  of  the  arch  slice  at  elevation  VI ; 
in  fact  it  practically  never  will  do  so,  as  perfectly  even  slopes  of  the  respective 
canyon  sides  or  walls  will  rarely  be  found.  Hence  the  shape  of  the  surface 
of  the  up-stream  face  of  the  dam  between  elevations  VI  and  V cannot  be 
described  as  resembling  that  of  any  geometrical  body.  Elevation  IV 
is  coincident  with  another  change  of  slope  in  the  sides  of  the  canyon ; and  the 
most  economical  mean  radius  corresponding  to  the  fixed  distance  W*  across 
ihe  canyon  at  this  level  is  found  in  the  same  manner  as  were 
found  the  mean  radii  for  elevations  VI  and  V ; and  the  location  of  the 
center  of  curvature  of  the  arch  slice  at  this  elevation  is  fixed,  regardless 
of  the  location  of  the  centers  of  the  slices  at  elevations  VI  and  V.  In  other 
words,  the  dam  has  no  common  center  line,  and  centers  are  located  principally 
with  a view  to  getting  the  length  of  the  arch  as  short  as  possible  for  a given 
distance  across  the  canyon.  The  radii  and  thicknesses  at  elevations  III,  II 
and  I are  correspondingly  determined  in  accordance  with  the  procedure  above 
outlined. 

So  far  only  the  average  stress  q has  been  considered.  Towards  lower  ele- 
vations where  the  thickness  t of  the  different  arch  slices  is  considerable,  it  is 
necessary  to  investigate  also  the  maximum  stress  to  be  sure  that  this  is  not 
above  the  safe  limit.  The  maximum  arch  compression  will  be  equal  to 


9* 


z(K-ht) 

ZFf  + ft 


and  will  exist  along  the  down-stream  edge.  The  stress  on  the  foundation  does 
not  need  to  be  considered  for  dams  of  this  type  less  than  200  ft.  in  height,  as 
it  will  always  be  within  the  safe  limit. 

The  above  described  method  of  design  can  also  be  directly  applied  to  tin' 
multiple  arch  type  of  dam.  In  this  case  the  most  economical  result  will  be 
obtained  by  taking  the  top  width  equal  the  distance  between  centers  of 
buttresses,  and  the  bottom  width  equal  the  distance  between  outside  of 
buttresses,  and  by  choosing  the  enclosed  angle  less  than  the  most  economical  at 
the  top  where  excess  thickness  must  be  provided  for  mechanical  reasons  and 
gradually  increasing  this  angle  towards  the  foundation. 


PAGE  NINE 


THE  DRAWING  UP 
OF  THE  DAM 

After  having  calculated  the  different  radii  and  respective  thicknesses  of  the 
several  horizontal  slices  of  the  dam,  the  top  thickness,  which  is  generally  chosen, 
is  set  off  and  the  arcs  of  two  concentric  circles  with  Radii  Rg  and  (Rc  -J-  to) 
respectively  are  drawn  in  on  the  contour  map ; and  the  centers  of  such  circles 
will  be,  of  course,  on  a line  drawn  perpendicular  to  the  center  of  the  chord  W*. 
The  thickness  ts  is  then  set  off ; and  the  arcs  of  the  two  other  concentric 
circles,  with  radii  Rs  and  (R*  + U)  respectively,  are  drawn  in  until  intersection 
occurs  with  the  contour  line  V — V,  bearing  in  mind  that  the  center  common 
to  these  latter  two  circles  does  not  need  to  be  on  the  perpendicular  to  the 
chord  Wo  above  referred  to.  These  four  circles,  concentric  only  in  pairs, 
determine  the  contour  of  the  dam  between  elevations  VI  and  V.  It  is  usually 
convenient  and  preferable  to  assume  the  dowmstream  faces  of  the  upper  slices 
of  the  dam  adjacent  the  center  thereof,  to  be  vertical,  at  least  for  the  first  trial ; 
although  after  the  lower  slices  have  been  laid  in,  it  may,  at  times,  be  found 
desirable  to  slope  the  central  portion  of  such  face  one  way  or  the  other.  The 
center  of  the  arch  slice  at  elevation  V — V is  correspondingly  located  on  a 
perpendicular  drawn  through  the  center  of  the  chord  W>;  and  the  thickness  b 
is  set  off,  assuming  initially  again  that  the  central  portion  of  the  down-stream 
face  is  substantially  vertical  here  also ; although  some  slope  may  thereafter  be 
given  to  it.  It  has  been  found  in  practice  that  a vertical  wall  at  this  point 
usually  affords  the  most  economical  construction.  At  other  points  the  down- 
stream face  will  always  have  some  slope,  due  to  the  above  method  of  de- 
sign. The  arcs  of  two  concentric  circles  with  radii  R^  and  (R*  -j-  ti) 
respectively  are  then  drawn  in  until  intersection  occurs  with  contour  lines 
IV — IV ; bearing  in  mind  again  that  the  center  common  to  these  two  circles 
does  not  need  to  and  hardly  ever  will  lie  on  a center  line  drawn  perpendicu- 
larly to  the  centers  of  either  chords  We  or  W». 

The  same  procedure  as  outlined  above  is  thereafter  followed  to  get  the 
up  and  down-stream  face  lines  at  elevations  III,  II  and  I. 

A certain  amount  of  discretion  must  be  exercised  in  locating  the  centers 
of  the  respective  arch  slices,  especially  where  a very  abrupt  change  occurs  at 
one  side  only  or  upon  one  wall  of  the  canyon. 

While  it  is  generally  preferable  to  so  form  the  slices  or  sectors 
of  the  dam,  which  lie  between  the  several  elevations,  that  the  tops 
and  bottoms  of  adjoining  slices  may  be  regarded  as  being  superposed  in  strict 
coincidence  in  the  manner  shown  in  figures  4 and  5,  it  is  desirable  in  some 
localities  to  face  the  dam  with  ashlar,  cut-stone  or  the  like,  and  it  may  be  of 
advantage  in  such  case  to  step  the  faces  of  the  dam  off  as  shown  in  the 
enlarged  section  A — B shown  in  figure  6.  The  dam  will  then  consist  of  a num- 

PAGE  TEN 


ber  of  cylindrical  rings  superposed  one  upon  the  other.  The  up  and  down 
stream  radii  in  such  case,  however,  are  ascertained  in  exactly  the  same  man- 
ner as  in  the  foregoing. 


As  the  dam  must  also  be  safe  with  reservoir  empty,  it  is  necessary  to  have 
t increase  from  the  crest  to  the  foundation  to  prevent  overhang.  The  pro- 
portional increase  in  water  pressure  must,  therefore,  be  greater  than  the 
proportional  decrease  in  length  of  the  up-stream  radius  as  we  proceed  towards 
the  foundation.  The  ratio  of  increase  in  water  pressure  is  always  fixed  and  the 
ratio  of  decrease  in  the  length  of  the  up-stream  radius  depends  upon  the  slope 
of  the  canyon  sides.  Now,  if  these  slopes,  are  such  that  at  any  intermediate  ele- 
vation the  ratio  of  decrease  in  length  of  the  up-stream  radius  (corresponding 
to  a 1 330  arch)  has  been  greater  than  the  ratio  of  increase  in  water  pressure,  a 
decrease  in  the  thickness  of  the  dam  at  this  elevation  would  result  and  the 
structure  would  be  overhanging.  If  a certain  thickness  must  be  provided  to 
prevent  overhanging,  it  is  most  economical  to  throw  normal  load  on  the  total 
area  by  increasing  the  length  of  the  up-stream  radius  above  that  corresponding 
to  a 133°  arch  for  the  reason  that  a flat  arch  requires  less  material  than  a more 
curved  one  of  the  same  thickness.  By  flattening  the  arch  the  enclosed  angle 
has  been  decreased  and  it  will  be  found  that  to  cover  all  practical  cases  the 
enclosed  angle  will  have  to  be  varied  between  the  limits  140°  and  6o°  in  order 
to  get  the  most  economical  dam,  and  one  which  also  will  satisfy  the  require- 
ments for  safety  with  no  water  in  the  reservoir. 


PAGE  ELEVEN 


MECHANICAL  FEATURES 

OF  STRUCTURE 


Besides  the  great  saving  in  material  this  type  of  dam  possesses  another 
feature  of  marked  importance.  This  feature  is  that  arch  action  can  and  will 
take  place  even  very  close  to  the  foundation,  for  the  following  reasons : 

When  an  arch  dam  of  any  type  is  loaded  it  deflects.  This  deflection  is  a 
maximum  at  the  crown  and  is  equal  to 


/> ( t'psi rfvtm  radius)' 

X fixt 

where  C is  a factor  which  takes  the  curved  beam  action  into  consideration ; 
E is  the  modulus  of  elasticity.  For  26  = 90°  C equals  one ; for  larger  angles  it 
is  above  one  (1.15  at  133°)  and  for  smaller  angles  it  is  below  one  (0.93  at  6o°J. 

From  this  formula  is  directly  seen  that  the  deflection  is  practically  pro- 
portional to  the  square  of  the  up-stream  radius  divided  by  the  thickness  t. 
P and  E are  constants,  so  far  as  the  comparison  of  the  two  types  is 
concerned.  The  new  type  of  dam  is  designed  with  decreasing  length  of  up- 
stream radius,  the  old  type  of  arch  dam  with  constant  length  of  radius,  or 
if  a face  batter  is  used,  with  increasing  length'of  radius  from  the  crest  towards 
the  foundation.  In  the  new  type  of  arch  dam  the  length  of  the  up-stream 
radius  near  the  foundation  may  be  only  one-third  of  what  it  is  at  the  crest. 
The  thickness  t may  be  only  one-half  of  the  thickness  required  for  the  old  type 
using  the  same  average  unit  compression.  The  resulting  deflection  of  the 
crown  near  the  foundation  will,  therefore,  be  2/9  or  about  1/5  of  what  it  would 
have  been  if  a constant  up-stream  radius  had  been  used.  In  other  words,  this 
new  type  acting  as  an  arch  is  able  to  take  up  5 times  as  much  of  the  load  near 
the  foundation  for  the  same  deflection  as  the  old  type.  For  the  small  deflection 
in  question  cantilever  or  gravity  action  cannot  predominate ; the  structure 
must  act  chiefly  as  an  arch  and  as  such  it  has  the  necessary  strength.  As  the 
dam  has  weight,  some  gravity  action  will  exist  and  in  the  upper 
sections,  where  the  arch  is  long  and  thin,  this  gravity  or  cantilever  action  will 
prevent  buckling  of  the  arch  before  crushing,  if  the  dam  cross  section  has  an 
area  not  less  than  one-half  that  of  an  ordinary  gravity  section,  designed  with 
a factor  of  safety  against  overturning  of  two. 

The  small  average  deflection  characteristic  of  this  new  type  of  dam  will 
make  it  possible  for  the  structure  to  take  care  of  stresses  due  to  temperature 
changes  and  shrinkage,  eliminating  cracks  either  entirely  or  to  a large  extent. 
Shrinkage  and  low  temperature  both  tend  to  shorten  the  length  of  the  arch 
the  same  as  the  load.  As  the  ends  of  the  arch  are  fixed  to  the  abutments,  this 
shortening  either  causes  cracks  to  develop  or  forces  the  crown  back.  In  this 

PAGE  TWELVE 


new  type  the  average  deflection  being  much  smaller  for  the  same  amount  of 
decrease  in  length  of  arch  than  in  the  old  type,  the  tension  necessary  to  cause 
this  deflection  may  not  exceed  the  ultimate  tensile  strength  of  the  concrete,  in 
which  case  no  cracks  would  develop.  In  any  event  cracks  are  not  as  liable 
to  occur  as  in  the  old  type. 


COMPARISON  WITH  EXISTING 

ARGH  DAMS 


The  Bear  Valley  dam  in  Southern  California,  so  often  cited  on  account 
of  its  boldness,  would,  if  reconstructed  according  to  the  foregoing  method, 
have  a factor  of  safety  of  over  12  at  its  weakest  point,  using  the  same  cross 
section,  or  it  would  have  a factor  of  safety  of  between  9 and  10  using  the 
same  amount  of  material  as  in  the  existing  dam  with  its  factor  of  safety  of  3 
as  follows : 

The  weakest  portion  of  the  Bear  Valley  dam  is  at  elevation  48  ft.  below 
the  crest;  here  the  thickness  is  8.42  ft.,  and,  as  the  length  of  the  up-stream 
radius  is  340  ft.  at  this  elevation,  the  mean  compression  per  square  inch  of  the 
masonry  is  found  from 

Water  pressure  x.  up-stream  rad.  48  x 62.5  x 340 

area  8.42  x 144  = ^4°  lbs., 

which  should  give  the  dam  a factor  of  safety  of  about  3.  The  length  of  the 
up-stream  radius  which  should  have  been  used  in  order  to  get  the  best  use  of 
the  material  is  160  ft.  at  the  top  instead  of  335  ft.  as  constructed. 
Suppose  this  radius  was  used  for  the  whole  face,  the  factor  of  safety  would 

340 

thereby  be  increased  from  3 to  7 x 3 = 6.37  at  the  weakest  point 

160'  370 

The  increase  in  material  due  to  the  longer  arch  would  amount  to , 

300 

or  23%  approximately,  while  the  factor  of  safety  has  been  more  than  doubled. 

If,  instead  of  using  a constant  up-stream  radius  of  160  ft.,  the  length  be 
changed  so  as  to  keep  the  enclosed  angle  as  close  as  possible  to  the  most 
economical  value,  a much  safer  structure  would  result.  At  elevation  48  ft. 
below  the  crest  the  length  of  the  up-stream  radius  would  be  80  ft.  or  less  (the 
exact  length  cannot  be  given  due  to  the  absence  of  a contour  map  of  the  site) 
instead  of  335  ft.  as  used. 

Using  the  same  thickness  of  section  as  before,  that  is,  8.42  ft.,  the  average 
compression  per  square  inch  at  this  the  weakest  portion  of  the  dam  can  be 
found  from 


PAGE  THIRTEEN 


Water  pressure  x up-stream  radius  48  x 62.5  x 80 

area  8.42x144  198  lbs. 


a unit  compression  4 Y\  times  smaller  than  the  one  used  in  the  structure. 
The  increase  in  material  due  to  the  longer  arch  will  be  about  one-third.  That 
is,  by  adding  34  per  cent  to  the  amount  of  material,  we  have  raised  the  factor 
of  safety  from  3 to  12^4.  Using  the  same  amount  of  material  the  new  type  of 


Lithgow  Coot  a mandril  Muiigee  Wollongong  Medlow 

N-l 


dam  would  show  a factor  of  safety  of  9.5  as  against  3 in  the  dam  as  constructed. 
This  goes  to  show  that  there  is  really  absolutely  no  boldness  about  the  cross 
section  used  in  the  Bear  Valley  dam.  The  cut  and  try  method  employed  in 
the  design,  however,  is  certainly  bold. 


IV/ rn  worth 


a 

v| 

^3.0 

— — 

pr 

I9_ 

Ml 

f%.  4.2  . 

\f>\ 

<c'V\ 

. <3.\ 

:<a  \ 

Wellington 


Parke# 


PAGE  FOURTEEN 


More  recently  there  has  been  constructed  a number  of  arched  dams  in 
New  South  Wales,  Australia,  which  attract  attention  on  account  of  the  thin- 
ness of  their  sections.  They  have,  however,  been  properly  designed  and, 
therefore,  possess  a sufficiently  high  factor  of  safety.  A full  description  of 
these  interesting  structures  can  be  found  in  a paper  read  by  their  designer, 
L.  A.  B.  Wade,  M.  I.  C.  E.,  before  the  Institution  of  Civil  Engineers,  and  from 
which  the  following  table  and  cross  sections  are  copied. 


Table  showing  Details  of  Curved  Masonry  Dams  built  by  the  Public  Works 
Department  of  New  South  Wales. 


Depth 

below 

Radius 

Limit 

Character  of 

Date 

Locality 

Max.  ht.  above 

Total 

Top 

Thick- 

of 

of  pres- 

rock forming 

of  con  - 

foundations 

Length 

thick- 

crest 

ness  of 

curved 

sure  in 

site  and  us&d 

at  ruction 

ft. 

ft. 

ness. 

ft. 

of  lop 
thickness. 

base 

ft. 

part 

ft. 

tons  • 
per  sq.ft. 

in  construction 

Li  thgow  No./ 

35.0 

178 

3.5 

3.5 

10.88 

100 

11.2 

Sandstone 

1806 

Par/Ces 

33.5 

540 

3.0 

6.0 

13.5 

300 

26.9 

Granite 

1897 

Cootam  an  ctra 

46.0 

640 

3.0 

8.0 

13.0 

250 

28.0 

Granite 

1898 

Tumworth 

61.0 

440 

3.0 

3.0 

21.5 

250 

22.4 

Granite 

1898 

Wellington 

46.0 

350 

3.0 

7.0 

10.0 

150 

22.4 

Conglomerate 

189.0 

Mudgee 

50.0 

498 

3.0 

5.0 

18.0 

253 

22.4 

Alter-ed  state 

1899 

Wot  longong 

42.0 

535 

3.5 

5.0 

11.62 

200 

22.4 

Da  sex  l f 

Lit  tigow  No.  2 

87.0 

221 

3.0 

3.0 

24.0 

too 

11.2 

Sandstone 

1906 

A ted  tow 

65.0 

124 

35 

21.0 

6.96 

60 

13.4 

Sandstone 

1906 

• Short  tMTus  of  2000  lbs. 


The  maximum  stresses  used  are  somewhat  higher  than  usual,  although 
only  half  of  what  they  are  in  the  Bear  Valley  dam.  Using  the  new  type 
described  above  for  these  sites  the  maximum  stresses  could  be  brought  down 
to  about  one-half  of  their  present  values,  resulting  in  still  safer  structures  with 
equal  amounts  of  material.  To  use  the  same  stresses  and,  therefore,  a thinner 
section  requiring  less  material  would  in  these  cases  perhaps  not  be  advisable 
as  the  original  sections  are  already  rather  thin. 

The  main  features  embodied  in  this  new  type  of  dam  have  been  patented 
and  the  rights  to  the  design  are  owned  by  F.  G.  BAUM  & COMPANY. 
Chronicle  Building,  San  Francisco,  Cal.,  who  are  prepared  to  furnish  complete 
designs  and  estimates,  and  supervise  the  construction.  The  charges  are  no 
higher  than  for  ordinary  engineering  work.  Should  the  owner  prefer  to  have 
his  dam  designed  and  built  by  his  own  force,  this  company  solicits  corre- 
spondence relative  to  the  use  of  this  design. 


PAGE  FIFTEEN 


